85.83 Chapter 10. Systems of differential equations and their applications. A Exercises at page 444

85.83.1 problem 1 (a)
85.83.2 problem 1 (b)
85.83.3 problem 1 (c)
85.83.4 problem 1 (d)
85.83.5 problem 1 (e)
85.83.6 problem 1 (f)
85.83.7 problem 1 (g)
85.83.8 problem 1 (h)
85.83.9 problem 3
85.83.10 problem 4 (a)
85.83.11 problem 4 (b)
85.83.12 problem 4 (c)
85.83.13 problem 4 (d)
85.83.14 problem 6